Efficient mass transfer is important to effectuate exchange of substances for chemical reactions, dialysis, and other chemical engineering processes. For example, there are hemodialysis systems depending on mass transport of metabolic products and/or ions across a membrane between blood and a dialysis fluid. These systems can remove toxic products from the blood and/or effectuate an ionic balance in the blood. Mass transfer within a fluid, and at boundaries of a fluid can be enhanced by energy and flow fields in the fluid. For example, input mechanical energy stirring a fluid, energy of flow in vortices, turbulence in a flow, or thermal energy, in single or in combination, can effectuate mass transfer and/or mixing.
Although the terms mixing and mass transfer are sometimes used synonymously, mass transfer as used herein refers to a flux of material from one spatial location to another, whereas mixing references the reduction of compositional differences through mass transfer. Mass transfer and mixing are often synergistic. For example, transfer of material into flowing fluid from a boundary, and/or transfer of material from a flowing fluid to a boundary, can be increased by mixing fluid near the boundary with different fluid in flow regions away from the boundary. Because the fluid in contact with a solid boundary has no tangential velocity (e.g. zero velocity boundary condition), transferring the material out of slow moving fluid near a boundary (e.g. in a boundary layer) can increase mass transfer rate.
Mass transport in the bulk of a fluid and/or mass transfer in a boundary layer can be enhanced by adding and/or transforming energy. For example, fluid can be mixed by introducing kinetic energy that moves one portion of fluid relative to another portion. In some apparatus, mixing has been induced using a source of external energy to driving a moving impeller. There is apparatus where kinetic and pressure energy of a flowing fluid is mixed using a static impeller (mixer) configuration. Energy effective for mixing can also be obtained through transformation of a relatively constant fluid motion into vortices, turbulence, and the like. For example, vortices can be formed in a sudden change in the cross section of a flow (e.g. at a boundary and/or surface discontinuity). When vortices are formed in this manner, energy from upstream fluid flow is transformed into energy for the vortex motion. Turbulence can also be generated with a sudden change in flow cross section. Where there is turbulence, pressure and/or kinetic energy of translational fluid motion is converted into chaotic flow and eddy currents. Turbulent flow can enhance mass transfer and mixing.
Energy in a flowing fluid can also be transformed into heat, sound, and/or electromagnetic radiation. Chaotic flows comprising vortices eddies, as well as collapsing gas bubbles, in a flow have been and are particularly favorable environments to effectuate such transformation. Furthermore, it has been found that various forms of energy release in a fluid can induce and/or enhance chemical reactions. For example, it has been found that acoustic energy, shock waves, and/or electromagnetic radiation in a fluid can stimulate chemical reactions. These and other forms of energy can be released in a flow comprising of vortices, turbulence, bubbles, and/or other forms of chaotic flow motion.
Chemical reaction in a fluid can be useful for destruction of dissolved toxins such as toxic compounds extracted in the dialysis of blood using a membrane. There are numerous other applications depending on chemical reaction in a fluid. For example, it has been found that chemical reactions of dissolved calcium compounds occurring on the surface of copper-containing alloys, are effective to improve water use efficiency for irrigation.
It can thereby be seen that there has been a long felt need for apparatus and methods to improve mixing and/or to induce chemical reactions in a fluid flow.